1. Field of the Invention
The present invention relates to an azo compound, an azo pigment, a pigment dispersion, a coloring composition, a coloring composition for color filters, a color filter, a method for preparing a coloring composition for color filters, an ink for inkjet recording, a printing ink, a coating material, a dye, and a resist ink.
2. Description of the Related Art
In recent years, materials for forming color images in particular are the mainstream image recording materials, and specifically, recording materials for an inkjet system, recording materials for a thermosensitive transfer system, recording materials for an electrophotographic system, transfer-type silver halide photosensitive materials, printing inks, recording pens, and the like are in active use. Furthermore, color filters are used to record and reproduce color images in image pickup elements such as a charge-coupled device (CCD) among imaging apparatuses, and in liquid crystal displays (LCDs) or plasma display panels (PDPs) among display apparatuses. In these color image recording materials or color filters, colorants (dyes or pigments) of the three primary colors of a so-called additive color mixing method or a so-called subtractive color mixing method are used to display or record full color images. However, in the current situation, there is no colorant which has absorption characteristics capable of realizing a preferable color reproduction gamut, and also has fastness that can withstand various use conditions and environmental conditions. Thus, there is a strong demand for an improvement.
The dyes and pigments that are used in the various applications described above need to have properties such as described below in common. That is, the properties include absorption characteristics that are preferable in terms of color reproducibility, and fastness under the environmental conditions used, for example, satisfactory light fastness, satisfactory heat resistance, and satisfactory resistance to oxidative gases such as ozone. In addition, when the colorant is a pigment, the pigment needs to have properties such as that the pigment substantially is insoluble in water or organic solvents and has satisfactory chemical resistant fastness, and that preferable absorption characteristics in a molecular dispersion state are not impaired even if the pigment is used in the form of particles. The requested characteristics described above can be controlled by the intensity of the intermolecular interaction, but since the two properties are in a trade-off relationship, it is difficult to achieve a balance between the two properties.
Furthermore, in addition to that, when such a pigment is put to use, there is also a need for properties such as that the pigment has a particle size and a particle shape necessary to exhibit desired transparency, that the pigment has satisfactory fastness under the environmental conditions used, for example, satisfactory light fastness, satisfactory heat resistance, satisfactory resistance to oxidative gases such as ozone, and satisfactory chemical resistant fastness against organic solvents or sulfurous acid gas, and that the pigment is dispersed even to a state of very fine particles in the medium used and maintains a stable dispersion state. Particularly, there is a strong demand for a pigment which has satisfactory hue, has high tinctorial strength even in the presence of light, heat and humidity, and an active gas in the environment, and has fastness to light.
That is, the performance required from a pigment extends over a variety of fields as compared with dyes of which having performance as coloring molecules is demanded, and the pigment needs to satisfy not only the performance as coloring molecules, but also the performance requested as a solid (fine particle dispersion) as aggregates of coloring molecules. Consequently, the group of compounds that can be used as pigments is extremely limited as compared with dyes, and even if high performance dyes are converted to pigments, not many of the dyes can satisfy the performance required as fine particle dispersions, and such pigments cannot be easily developed. This is verified from the fact that the number of pigments registered with the Color Index does not make up even 1/10 of the number of dyes.
Since azo pigments have excellent color and tinctorial strength, which are chromatic characteristics, azo pigments are widely used in printing inks, inkjet inks, electrophotographic materials, and the like. Among these, azo pigments that are most typically used include diarylide yellow pigments and naphthol red azo pigments. Examples of diarylide pigments include C.I. Pigment Yellow 12, Yellow 13, and Yellow 17. Examples of naphthol azo pigments include C.I. Pigment Red 208, and Red 242. However, since these pigments have very inferior fastness, particularly light fastness, when print materials are exposed to light, the pigments are degraded and discolorized, so that the pigments are not suitable for long-term storage of print materials.
In order to ameliorate such defects, there have been disclosed azo pigments having improved fastness by increasing the molecular weight or by introducing a group having a strong intermolecular interaction (see, for example, WO 2005/052074 A, WO 00/023525 A, and JP 2008-013472A). However, even for the improved pigments, for example, the pigment described in WO 2005/052074 A has light fastness that has been improved but is not yet sufficient, and for example, the pigments described in WO 00/023525A and JP 2008-013472A have a defect that the pigments have greenish color, low tinctorial strength, and inferior chromatic characteristics.
Furthermore, JP 1997-511278T (JP H09-511278T), JP 2008-007732A, JP 2004-123866A, and JP 3894726B disclose colorants having absorption characteristics with excellent color reproducibility and sufficient fastness. However, the specific compounds described in these patent documents either have satisfactory hues with inferior fastness, or satisfactory fastness with inferior hues. Also, the compounds easily dissolve in organic solvents or water, and do not therefore have sufficient chemical resistant fastness.
In the case of expression of full color by using a subtractive color mixing method based on three colors of yellow, magenta and cyan, or based on four colors of the three colors plus black, if a pigment of only one color having inferior fastness is used, the grey balance of the print material changes with a lapse of time. Also, if a pigment having inferior chromatic characteristics is used, color reproducibility at the time of printing is deteriorated. Therefore, in order to obtain a print material which maintains high color reproducibility for a long time period, a pigment and a pigment dispersion which can achieve a balance between chromatic characteristics and fastness are desirable.
Azo colorants have conventionally been utilized as colorants in various fields, since many of azo colorants have various visible light absorptions. For example, they have come into use in various fields such as coloration of synthetic resins, printing inks, colorants for sublimation type thermosensitive transfer materials, inks for inkjet recording, and colorants for color filters. Major performances required from azo colorants as colorants include the absorption spectrum. The hue of a colorant exerts a great influence on the tint and the tactile feeling of a body colored with the colorant, and gives a large effect on visual sensation. Therefore, studies have been conducted for a long time on the absorption spectra of colorants.
Conventionally known azo dyes containing a nitrogen-containing, 5-membered ring as an azo component are also disclosed in JP 2008-007732A. Furthermore, JP 2004-123866A, JP 3894726B, and JP 2592271B disclose naphthol-based azo pigments and dyes in which a benzene ring and a naphthalene ring are bonded through an azo group.
Furthermore, in recent years, there has been a demand for image display apparatuses to have miniaturization, thickness reduction, weight reduction, screen enlargement, definition enhancement and the like. Also, the range of applications of the image display apparatuses has expanded to displays for personal computers, television sets, game machines and the like, and the demand for color liquid crystal displays is rapidly increasing.
Under such circumstances, there are demands for the color filters used in liquid crystal display elements to have high color purity.
Known examples of color filters that are formed on elements in order to chromatize solid-state image pickup elements or liquid crystal display elements, include a color filter composed of a yellow filter layer, a magenta filter layer and a cyan filter layer that are formed adjacently to each other in the same plane on a substrate, and a color filter composed of a red filter layer, a green filter layer, and a blue filter layer.
In recent years, a further increase in definition has become desirable in color filters. However, since conventional pigment dispersion systems have a problem that the resolution does not improve, and unevenness occurs due to coarse particles of the pigment, the conventional pigment dispersion systems are not suitable for the applications where fine patterns are required, such as in solid-state image pickup elements. In order to solve this problem, it has been traditionally suggested to use dyes (see, for example, JP 1994-075375A (JP H06-75375A)).
Also, it is known that a red dye is used in the red filter array of a color filter (see, for example, JP 1993-005067A (JP H05-005067A)).
However, colored patterns obtained by using dyes do not exhibit sufficient heat resistance and light fastness. Therefore, investigations have been conducted on color filters using organic pigments which have excellent heat resistance and light fastness.
Examples of the method for producing a color filter which uses an organic pigment include a photolithographic method (see, for example, JP 1989-152449A (JP H01-152449A)) in which a process of performing patterning by exposing and developing a composition having an organic pigment dispersed in a photosensitive resin is repeated a necessary number of times, and printing methods such as offset printing and inkjet printing, in which an ink containing an organic pigment is used.
Use of organic pigments having excellent heat resistance and light fastness, such as anthraquinone-based pigments, diketopyrrolopyrrole-based pigments, quinacridone-based pigments, isoindoline-based pigments, perinone-based pigments, perylene-based pigments, and condensed azo-based pigments, has been taken into consideration. However, there is a problem that these pigments are generally not easily dispersed in color filters, and it is difficult to obtain a color filter having high transparency.
Similarly, for color filters composed of a yellow filter layer, a magenta filter layer and a cyan filter layer, a further improvement of fastness is desirable for the yellow colorant used in yellow filter layers.
Furthermore, WO 05/052074 A proposes a red ink composition for color filters containing a monoazo compound containing a naphthalene ring. However, a color filter using the compound described in WO 05/052074 A is not satisfactory in terms of contrast, and an increase in contrast is desired.